1. Field of the Invention
The present invention relates to wireless communications, and more particularly, to a method and apparatus for transmitting signals in a multi-node system.
2. Related Art
A data transfer amount of a wireless network has been rapidly increased in recent years. It is because various devices, e.g., a smart phone, a tablet personal computer (PC), or the like, that require machine-to-machine (M2M) communication and a high data transfer amount have been introduced and propagated. To satisfy the required high data transfer amount, a carrier aggregation (CA) technique, a recognition radio (CR) technique, or the like for effectively using more frequency bands, and a multiple antenna technique, a multiple base station cooperation technique, or the like for increasing data capacity within a limited frequency have recently drawn attention.
In addition, the wireless network has been evolved in a direction of increasing density of a node capable of accessing to an area around a user. Herein, the node implies an antenna (or antenna group) which is separated from a distributed antenna system (DAS) by a certain distance or farther. However, the node is not limited to this definition, and thus can also be used in a broader sense. That is, the node may be a macro eNB, a pico-cell eNB (PeNB), a home eNB (HeNB), a remote radio head (RRH), a remote radio unit (RRU), a relay, a distributed antenna (group), etc. A wireless communication system having nodes with higher density can provide higher system performance through cooperation between the nodes. That is, better system performance can be achieved when one base station controller manages transmission and reception of respective nodes and thus the nodes operate as if they are antennas or an antenna group for one cell, in comparison with a case where the respective nodes operate without cooperating with each other. Hereinafter, a wireless communication system including a plurality of nodes and an eNB for controlling the plurality of nodes is referred to as a multi-node system.
The plurality of nodes in the multi-node system can include at least one or more transmit antennas, and the eNB can transmit a signal by using two or more transmit antennas of the at least one or more nodes. That is, the multi-node system can operate based on multi input multi output (MIMO).
When the conventional wireless communication system operates based on MIMO, the eNB maps a codeword to a layer, and maps the layer to an antenna port and thereafter transmits it through a transmit antenna. In the conventional method, a fixed codeword-to-layer mapping (CLM) is used when the number of layers and the number of codewords are determined. When the conventional method is equally applied to the multi-node system, there is a problem in that flexibility of signal transmission deteriorates due to the fixed CLM.
Accordingly, there is a need for a new CLM method and transmission apparatus applicable to a multi-node system.